Thrust efficient turbofan engine

ABSTRACT

A turbofan engine according to an exemplary embodiment of this disclosure, among other possible things includes a gas generator section for generating a gas stream flow with higher energy per unit mass flow than that contained in ambient air. A power turbine converts the gas stream flow into shaft power. The power turbine rotates at a first rotational speed. A speed reduction device is driven by the power turbine. A propulsor section includes a fan driven by the power turbine through the speed reduction device at a second speed lower than the first speed for generating propulsive thrust as a mass flow rate of air through a bypass flow path. The fan includes a tip diameter greater than about fifty (50) inches and an Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of the mass flow rate of air through the bypass flow path, a tip diameter of the fan and the first rotational speed of the power turbine is less than about 0.30 at a take-off condition.

REFERENCE TO RELATED APPLICATION

The present disclosure is a continuation of U.S. application Ser. No.13/854,225 filed on Apr. 1, 2013, which claims priority to U.S.Provisional Application No. 61/787,321 filed on Mar. 15, 2013.

BACKGROUND

A turbofan engine typically includes a fan section, a compressorsection, a combustor section and a turbine section. Air entering thecompressor section is typically compressed and delivered into thecombustor section where it is mixed with fuel and ignited to generate ahigh-pressure, high-temperature gas flow. The high-pressure,high-temperature gas flow expands through the turbine section to drivethe compressor and the fan section.

A direct-drive turbofan engine typically includes a fan section directlydriven by a low pressure turbine producing the power needed to drive thefan section, such that the low pressure turbine and the fan sectionrotate at a common rotational speed in a common direction. A powertransmission device such as a gear assembly or other mechanism may beutilized to drive the fan section such that the fan section may rotateat a speed different than the turbine section so as to increase theoverall efficiency of the engine. In a gear-drive turbofan enginearchitecture, a shaft driven by one of the turbine sections may providean input to the speed reduction device that drives the fan section at areduced speed such that both the turbine section and the fan section canrotate at closer to their respective optimal rotational speeds.

SUMMARY

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a gas stream flow with higher energy per unit mass flowthan that contained in ambient air. A power turbine converts the gasstream flow into shaft power. The power turbine rotates at a firstrotational speed. A speed reduction device is driven by the powerturbine. A propulsor section includes a fan driven by the power turbinethrough the speed reduction device at a second speed lower than thefirst speed for generating propulsive thrust as a mass flow rate of airthrough a bypass flow path. The fan includes a tip diameter greater thanabout fifty (50) inches and an Engine Unit Thrust Parameter (“EUTP”)defined as net engine thrust divided by a product of the mass flow rateof air through the bypass flow path, a tip diameter of the fan and thefirst rotational speed of the power turbine is less than about 0.30 at atake-off condition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.25 at the take-take off condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP is less than about 0.20 at the take-off condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.10.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.08.

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is greater than about 50 inches and less thanabout 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/hour and about 80,000 lbm/hour.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the power turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thepropulsive thrust generated by the turbofan engine is between about16,000 lbf and about 120,000 lbf.

In a further embodiment of any of the foregoing turbofan engines, thegas generator defines an overall pressure ratio of between about 40 andabout 80.

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a gas stream flow with higher energy per unit mass flowthan that contained in ambient air. A power turbine converts the gasstream flow into shaft power. The power turbine rotates at a firstrotational speed. A speed reduction device is driven by the powerturbine. A propulsor section includes a fan driven by the power turbinethrough the speed reduction device at a second speed lower than thefirst speed for generating propulsive thrust as a mass flow rate of airthrough a bypass flow path. The fan includes a fan tip diameter greaterthan about fifty (50) inches and an Engine Unit Thrust Parameter(“EUTP”) defined as net engine thrust divided by a product of the massflow rate of air through the bypass flow path, a tip diameter of the fanand the first rotational speed of the power turbine is less than about0.15 at one of a climb condition and a cruise condition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.125 for at least one of the climb condition and thecruise condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of the climb condition and the cruise condition is less thanabout 0.08.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at a take-off condition is less than about 0.15.

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is between about 50 inches and about 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/hour and about 80,000 lbm/hour.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the power turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thepropulsive thrust generated by the turbofan engine is between about16,000 lbf and about 120,000 lbf.

In a further embodiment of any of the foregoing turbofan engines, thegas generator defines an overall pressure ratio of between about 40 andabout 80.

A turbofan engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a gas generator sectionfor generating a high energy gas stream. The gas generating sectionincludes a compressor section, combustor section and a first turbine. Asecond turbine converts the high energy gas stream flow into shaftpower. The second turbine rotates at a first speed and includes lessthan or equal to about six (6) stages. A geared architecture is drivenby the second turbine. A propulsor section is driven by the secondturbine through the geared architecture at a second speed lower than thefirst speed. The propulsor section includes a fan with a pressure ratioacross the fan section less than about 1.45. The propulsor sectiongenerates propulsive thrust as a mass flow rate of air through a bypassflow path from the shaft power. The fan includes a tip diameter greaterthan about fifty (50) inches and an Engine Unit Thrust Parameter(“EUTP”) defined as net engine thrust divided by a product of a massflow rate of air through the bypass flow path, a tip diameter of the fanand the first rotational speed of the second turbine is less than about0.30 at a take-off condition.

In a further embodiment of the foregoing turbofan engine, the EUTP isless than about 0.25 at the take-off condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP is less than about 0.20 at the take-off condition.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at one of a climb condition and a cruise condition is less thanabout 0.10.

In a further embodiment of any of the foregoing turbofan engines, theEUTP at the take-off condition is less than about 0.08.

In a further embodiment of any of the foregoing turbofan engines, thefan section defines a bypass airflow having a bypass ratio greater thanabout ten (10).

In a further embodiment of any of the foregoing turbofan engines, thetip diameter of the fan is between about 50 inches and about 160 inches.

In a further embodiment of any of the foregoing turbofan engines, themass flow generated by the propulsor section is between about 625lbm/hour and about 80,000 lbm/hour.

In a further embodiment of any of the foregoing turbofan engines, thefirst speed of the second turbine is between about 6200 rpm and about12,500 rpm.

In a further embodiment of any of the foregoing turbofan engines, thesecond turbine comprises a low pressure turbine with 3 to 6 stages.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example turbofan engine.

FIG. 2 is a schematic view of functional elements of the exampleturbofan engine.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes a fan section 22, a compressor section 24, a combustor section26 and a turbine section 28. Alternative engines might include anaugmenter section (not shown) among other systems or features. The fansection 22 drives air through a bypass flow path B while the compressorsection 24 draws air in along a core flow path C where air is compressedand communicated to a combustor section 26. In the combustor section 26,air is mixed with fuel and ignited to generate a high pressure exhaustgas stream that expands through the turbine section 28 where energy isextracted and utilized to drive the fan section 22 and the compressorsection 24.

Although the disclosed non-limiting embodiment depicts a two-spoolturbofan gas turbine engine, it should be understood that the conceptsdescribed herein are not limited to use with two-spool turbofans as theteachings may be applied to other types of turbine engines; for examplea turbine engine including a three-spool architecture in which threespools concentrically rotate about a common axis and where a low spoolenables a low pressure turbine to drive a fan via a speed reductiondevice such as a gearbox, an intermediate spool that enables anintermediate pressure turbine to drive a first compressor of thecompressor section, and a high spool that enables a high pressureturbine to drive a high pressure compressor of the compressor section.

The example engine 20 generally includes a low speed spool 30 and a highspeed spool 32 mounted for rotation about an engine central longitudinalaxis A relative to an engine static structure 36 via several bearingsystems 38. It should be understood that various bearing systems 38 atvarious locations may alternatively or additionally be provided and thatthe location of the bearing systems 38 may be varied as appropriate tothe application.

The low speed spool 30 generally includes an inner shaft 40 thatconnects a fan 42 and a low pressure (or first) compressor section 44 toa low pressure (or first) turbine section 46. The inner shaft 40 drivesthe fan 42 through a speed change device, such as a geared architecture48, to drive the fan 42 at a lower speed than the low speed spool 30.The high-speed spool 32 includes an outer shaft 50 that interconnects ahigh pressure (or second) compressor section 52 and a high pressure (orsecond) turbine section 54. The inner shaft 40 and the outer shaft 50are concentric and rotate via the bearing systems 38 about the enginecentral longitudinal axis A.

A combustor 56 is arranged between the high pressure compressor 52 andthe high pressure turbine 54. In one example, the high pressure turbine54 includes at least two stages to provide a double stage high pressureturbine 54. In another example, the high pressure turbine 54 includesonly a single stage. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine. It will be appreciated that each of thepositions of the fan section 22, compressor section 24, combustorsection 26, turbine section 28, and fan drive gear system 48 may bevaried. For example, gear system 48 may be located aft of combustorsection 26 or even aft of turbine section 28, and fan section 22 may bepositioned forward or aft of the location of gear system 48.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about five (5). The pressure ratio of the example low pressureturbine 46 is measured prior to an inlet of the low pressure turbine 46as related to the pressure measured at the outlet of the low pressureturbine 46 prior to an exhaust nozzle.

A mid-turbine frame 58 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 58 further supports bearing systems 38in the turbine section 28 as well as setting airflow entering the lowpressure turbine 46.

Airflow through the core airflow path C is compressed by the lowpressure compressor 44 then by the high pressure compressor 52 mixedwith fuel and ignited in the combustor 56 to produce a gas stream withhigh energy that expands through the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 58 includes vanes 60, whichare in the core airflow path C and function as an inlet guide vane forthe low pressure turbine 46. Utilizing the vane 60 of the mid-turbineframe 58 as the inlet guide vane for low pressure turbine 46 decreasesthe length of the low pressure turbine 46 without increasing the axiallength of the mid-turbine frame 58. Reducing or eliminating the numberof vanes in the low pressure turbine 46 shortens the axial length of theturbine section 28. Thus, the compactness of the gas turbine engine 20is increased and a higher power density may be achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example speedreduction device is a geared architecture 48 however other speedreducing devices such as fluid or electromechanical devices are alsowithin the contemplation of this disclosure. The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 1.8 and, in some embodiments,greater than about 4.5.

In one disclosed embodiment, the gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of the low pressurecompressor 44. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a gas turbine engineincluding a geared architecture and that the present disclosure isapplicable to other gas turbine engines.

A significant amount of thrust is provided by airflow through the bypassflow path B due to the high bypass ratio. The fan section 22 of theengine 20 is designed for a particular flight condition—typically cruiseat about 0.8 Mach and about 35,000 feet. The flight condition of 0.8Mach and 35,000 ft., with the engine at its best fuel consumption—alsoknown as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—isthe industry standard parameter of pound-mass (lbm) of fuel per hourbeing burned divided by pound-force (lbf) of thrust the engine producesat that minimum point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodimentthe low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram °R)/(518.7° R)]^(0.5). The “Low corrected fan tip speed”, as disclosedherein according to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about twenty-six (26) fan blades. Inanother non-limiting embodiment, the fan section 22 includes less thanabout twenty (20) fan blades. Moreover, in one disclosed embodiment thelow pressure turbine 46 includes no more than about six (6) stagesschematically indicated at 34. In another non-limiting exampleembodiment the low pressure turbine 46 includes about three (3) stages.A ratio between the number of fan blades 42 and the number of lowpressure turbine rotors is between about 3.3 and about 8.6. The examplelow pressure turbine 46 provides the driving power to rotate the fansection 22 and therefore the relationship between the number of stages34 in the low pressure turbine 46 and the number of blades 42 in the fansection 22 defines an example gas turbine engine 20 with increased powertransfer efficiency.

Referring to FIG. 2, with continued reference to FIG. 1, the exampleturbofan engine 20 includes a gas generator section 62 for generating ahigh energy (per unit mass) gas stream 78. A power turbine 76 convertsthe high energy gas stream 78 into shaft power that drives the gearedarchitecture 48. In one embodiment, the power turbine may be the lowpressure turbine 46 that drives the inner shaft 40. The power turbine 76drives a propulsor section 64 through the geared architecture 48. Thepropulsor section 64 generates a mass flow 70 of air through the bypassflow path B that is a substantial portion of the overall propulsivethrust 68 generated by the turbofan engine 20.

The gas generator section 62 includes part of the fan sectioncompressing the air flow directed along the core flow path C, the lowpressure compressor 44, the high pressure compressor 52, the combustor56, the high pressure turbine 54 and part of the low-pressure turbine46. The high pressure turbine 54 is the first turbine after thecombustor 56 and drives the high pressure compressor 52. Disclosedexample gas generators include an overall pressure ratio betweenentering airflow and the exiting gas stream of between about 40 and 80.

The power driving the geared architecture 48 and thereby the propulsorsection 64 is provided by the power turbine 76. In this disclosure, thepower turbine 76 comprises the second turbine downstream of thecombustor 56 such as the low pressure turbine 46. The low pressureturbine 46 rotates at the first speed 72 and includes no more than six(6) stages 34. Moreover, the low pressure turbine 46 may include betweenthree (3) and six (6) stages 34, inclusive.

The power or low pressure turbine 46 rotates at the first speed 72(measured in terms of revolutions per minute) greater than a secondspeed 74 (also measured in terms of revolutions per minute) at which thefan section 22 rotates. In some embodiments, the first speed may bebetween about 6200 rpm and about 12,500 rpm. The first speed of the lowpressure turbine 46 is enabled by the speed reduction provided by thegeared architecture 48. At the first speed 72, each of the stages 34 aremore efficient at converting energy from the gas flow 78 to powertransmitted through the inner shaft 40.

The propulsor section 64 includes the fan section with fan blades 42that rotate about the engine axis A. The fan blades 42 extend radiallyoutward to define a tip diameter 66 between tips of opposing blades 42.The disclosed fan section 22 includes a tip diameter 66 that, in someembodiments, may be between about 45 inches (114 cm) and about 160inches (406 cm). In another example embodiment, the tip diameter 66 isbetween about 50 inches (127 cm) and about 85 inches (215.9 cm). The tipdiameter of the fan section 22 enables the desired fan pressure ratio incombination with the second rotational speed 74 provided by the gearreduction of the geared architecture 48.

The propulsor section 64 includes the fan section 22, and also includesthe fan exit guide vanes 80 and typically a fan nozzle 82. The fansection 22 is rotated at the second speed 74 by the geared architecture48 at a speed determined to enable the generation of the mass flow 70through the bypass flow path B. The pressure ratio across the fansection enables the efficient transformation of the shaft power providedin the power turbine 76 to propulsive thrust.

Fan pressure ratios below about 1.5, and better below 1.45 enabledesirable generation of thrust. The desired fan pressure ratio can beobtained utilizing a combination of fan exit guide vanes 80 and the fannozzle 82 that cooperate with the fan section 22 to enable fan pressureratios of less than 1.45. The mass flow 70 produced by the examplepropulsor section 64 may, in some embodiments, be between about 625lbm/hour (283 kg/hour) and about 80,000 lbm/hour (36,287 kg/hour). Themass flow of air 70 through the bypass flow path B combines with thrustgenerated by gas flow 78 to provide the overall engine thrust 68.However, a majority of engine thrust is provided by the mass flow of air70 generated by the propulsor section 64.

The overall efficiency of the turbofan engine 20 is a combination of howwell each of the sections 62, 76 and 64 converts input energy into thedesired output. The gas generator section 62 transforms energy from theair/fuel mixture ignited in the combustor 56 into the high-energy gasstream 78. The power turbine 46 converts energy from the gas stream 78into shaft power rotating the inner shaft 40 at a first speed 72 todrive the propulsor 64. The propulsor section 64 generates the mass flowof air 70 through bypass flow path B that provides the propulsive thrust68.

The thrust generation efficiency of the engine is related to the EngineUnit Thrust Parameter (“EUTP”), which is defined as the net thrustproduced by the engine divided by the product of mass flow rate of airthrough the fan bypass section, the fan tip diameter and the rotationalspeed of the power turbine section, as set out in Equation 1.

$\begin{matrix}{{{Engine}\mspace{14mu}{Unit}\mspace{14mu}{Thurst}\mspace{14mu}{Parameter}} = \frac{{Net}\mspace{14mu}{Thrust}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{Engine}}{\begin{bmatrix}( {{mass}\mspace{14mu}{flow}\mspace{14mu}{rate}\mspace{14mu}{of}\mspace{14mu}{air}\mspace{14mu}{through}\mspace{14mu}{fan}\mspace{14mu}{bypass}} ) \\( {{Fan}\mspace{14mu}{Tip}\mspace{14mu}{Diameter}} ) \\( {{Speed}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{power}\mspace{14mu}{turbine}} )\end{bmatrix}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The EUTP is a dimensionless quantity calculated utilizing the net enginethrust, the mass flow rate of air, the tip diameter and the powerturbine rotational speed expressed in appropriate units. For example, ifthe SI system of units is used, the units for these four quantities willbe N, kg/s, m and radians/s, respectively. The calculation of the EUTPwill be straight forward with no need to use conversion factors. If a“customary” set of units are used, i.e., engine thrust expressed in lbf,mass flow rate expressed in lbm/s, fan diameter express in inches androtational speed expressed in RPM, then the ratio calculated using thesevalues are multiplied by constant approximately equal to 3686.87 toaccount for all conversion factors necessary to get all parameters inself-consistent units.

Embodiments of the geared gas turbine engine 20 including the disclosedfeatures and configurations produce thrust ranging between about 16,000lbf (71,171 N) and about 120,000 lbf (533,786 N). The EUTP for thedisclosed turbofan engine 20 is less than those provided in prior artturbine engines. Three disclosed exemplary engines which incorporatepower turbine and propulsor sections as set forth in this applicationare described and contrasted with prior art engine examples in Table 1.

TABLE 1 Engine 1 Engine 2 Engine 3 Prior Art Engine 1 Prior Art Engine 2Fan Diameter in 55.9 73.0 81.0 63.5 49.2 Thrust Class lbf 17K 23.3K 33K33K 21K Max Climb Thrust lbf 3526 4878 6208 9721 8587 Fan face corr.Flow lbm/sec 703.4 1212.1 1512.4 847.0 502.6 Fan OD corr. Flow lbm/sec626.3 1108.8 1388.6 696.4 314.2 Fan face physical flow lbm/sec 261.5450.6 561.7 519.4 308.8 Fan OD physical flow lbm/sec 232.7 412.1 515.6426.9 193.1 Second speed (fan) RPM 4913 3377 3099 4969 7640 First speed(power turbine) RPM 11835 10341 9491 4969 7640 Engine Unit ThrustParameter 0.08 0.06 0.06 0.27 0.44 Average Cruise Thrust lbf 2821 39294729 5300 4141 Fan face corr. Flow lbm/sec 668.3 1157.6 1429.4 845.6490.5 Fan OD corr. Flow lbm/sec 598.0 1065.6 1322.6 695.5 312.1 Fan facephysical flow lbm/sec 254.1 440.2 543.4 327.4 181.1 Fan OD physical flowlbm/sec 227.3 405.2 502.7 269.2 115.2 Second speed (fan) RPM 4472 30702748 4769 6913 First speed (power turbine) RPM 10774 9402 8416 4769 6913Engine Unit Thrust Parameter 0.08 0.05 0.05 0.24 0.39 Max Takeoff Thrustlbf 12500 18735 25678 25382 17941 Fan face corr. Flow lbm/sec 610.01032.5 1438.8 871.1 496.6 Fan OD corr. Flow lbm/sec 546.6 948.5 1330.2711.8 312.1 Fan face physical flow lbm/sec 611.0 1029.4 1452.2 901.5509.4 Fan OD physical flow lbm/sec 547.4 945.6 1342.4 736.1 320.2 Secondspeed (fan) RPM 4689 3249 3117 5411 7791 First speed (power turbine) RPM11295 9951 9546 5411 7791 Engine Unit Thrust Parameter 0.13 0.10 0.090.37 0.54

In some example embodiments, the EUTP is as low as 0.05 at a cruisecondition and less than about 0.10 at maximum takeoff thrust. In anotherengine embodiment including a fan tip diameter greater than about fifty(50) inches the EUTP is less than about 0.30 at maximum takeoff thrust.In another engine embodiment including the fan tip diameter greater thanabout fifty (50) inches, the EUTP is less than about 0.25. In still afurther engine embodiment including a fan tip diameter greater thanabout fifty (50) inches, the EUTP is less than about 0.20.

In a further embodiment, the EUTP is less than about 0.08 at a cruiseand/or a climb condition. In one engine embodiment including a fan tipdiameter greater than about fifty (50) inches, the EUTP is less thanabout 0.15 at a cruise and/or climb condition. In another engineembodiment including a fan tip diameter of greater than about fifty (50)inches, the EUTP is less than about 0.125 at a cruise and/or climbcondition.

Moreover, the EUTP is accomplished through the use of the gearedarchitecture 48 at a gear ratio of, in some embodiments, greater thanabout 2.3. In other embodiments, the gear ratio may be greater thanabout 2.8. Accordingly, a ratio of the EUTP to the gear ratio furtherdefines physical operating characteristics of the disclosed engines. Inone disclosed embodiment, a ratio of the EUTP at takeoff to a gear ratioof 2.8 is about 0.028. In another disclosed ratio of the EUTP at a climbor cruise condition to the gear ratio of 2.8 is between about 0.036 and0.054.

Accordingly, the EUTP for engines based upon the disclosed features maybe less than 0.30 when the engine is operating at take-off condition,while it may have a value less than 0.1 when operating at climb andcruise conditions.

Accordingly, the disclosed embodiments of each of the gas generator 62,power turbine 76 and propulsor sections 64 of the geared engineembodiments efficiently convert energy to provide a more thrustefficient turbofan engine as compared to conventional non-gearedengines.

Although various example embodiments have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this disclosure. For that reason, thefollowing claims should be studied to determine the scope and content ofthis disclosure.

What is claimed is:
 1. A turbofan engine comprising: a gas generatorsection for generating a gas stream flow with higher energy per unitmass flow than that contained in ambient air; a power turbine convertingthe gas stream flow into shaft power, the power turbine rotating at afirst rotational speed; a speed reduction device driven by the powerturbine; and a propulsor section including a fan driven by the powerturbine through the speed reduction device at a second speed lower thanthe first speed for generating propulsive thrust as a mass flow rate ofair through a bypass flow path, wherein the fan includes a tip diametergreater than about fifty (50) inches and an Engine Unit Thrust Parameter(“EUTP”) defined as net engine thrust divided by a product of the massflow rate of air through the bypass flow path, a tip diameter of the fanand the first rotational speed of the power turbine is less than about0.30 at a take-off condition.
 2. The turbofan engine as recited in claim1, wherein the EUTP is less than about 0.25 at the take-take offcondition.
 3. The turbofan engine as recited in claim 1, wherein theEUTP is less than about 0.20 at the take-off condition.
 4. The turbofanengine as recited in claim 1, wherein the EUTP at one of a climbcondition and a cruise condition is less than about 0.10.
 5. Theturbofan engine as recited in claim 1, wherein the EUTP at one of aclimb condition and a cruise condition is less than about 0.08.
 6. Theturbofan engine as recited in claim 1, wherein the tip diameter of thefan is greater than about 50 inches and less than about 160 inches. 7.The turbofan engine as recited in claim 1, wherein the mass flowgenerated by the propulsor section is between about 625 lbm/hour andabout 80,000 lbm/hour.
 8. The turbofan engine as recited in claim 1,wherein the first speed of the power turbine is between about 6200 rpmand about 12,500 rpm.
 9. The turbofan engine as recited in claim 1,wherein the propulsive thrust generated by the turbofan engine isbetween about 16,000lbf and about 120,000 lbf.
 10. The turbofan engineas recited in claim 1, wherein the gas generator defines an overallpressure ratio of between about 40 and about
 80. 11. A turbofan enginecomprising: a gas generator section for generating a gas stream flowwith higher energy per unit mass flow than that contained in ambientair; a power turbine converting the gas stream flow into shaft power,the power turbine rotating at a first rotational speed; a speedreduction device driven by the power turbine; and a propulsor sectionincluding a fan driven by the power turbine through the speed reductiondevice at a second speed lower than the first speed for generatingpropulsive thrust as a mass flow rate of air through a bypass flow path,wherein the fan includes a fan tip diameter greater than about fifty(50) inches and an Engine Unit Thrust Parameter (“EUTP”) defined as netengine thrust divided by a product of the mass flow rate of air throughthe bypass flow path, a tip diameter of the fan and the first rotationalspeed of the power turbine is less than about 0.15 at one of a climbcondition and a cruise condition.
 12. The turbofan engine as recited inclaim 11, wherein the EUTP is less than about 0.125 for at least one ofthe climb condition and the cruise condition.
 13. The turbofan engine asrecited in claim 11, wherein the EUTP at one of the climb condition andthe cruise condition is less than about 0.08.
 14. The turbofan engine asrecited in claim 11, wherein the EUTP at a take-off condition is lessthan about 0.15.
 15. The turbofan engine as recited in claim 11, whereinthe tip diameter of the fan is between about 50 inches and about 160inches.
 16. The turbofan engine as recited in claim 11, wherein the massflow generated by the propulsor section is between about 625 lbm/hourand about 80,000 lbm/hour.
 17. The turbofan engine as recited in claim11, wherein the first speed of the power turbine is between about 6200rpm and about 12,500 rpm.
 18. The turbofan engine as recited in claim11, wherein the propulsive thrust generated by the turbofan engine isbetween about 16,000 lbf and about 120,000 lbf.
 19. The turbofan engineas recited in claim 11, wherein the gas generator defines an overallpressure ratio of between about 40 and about
 80. 20. A turbofan enginecomprising: a gas generator section for generating a high energy gasstream, the gas generating section including a compressor section,combustor section and a first turbine; a second turbine converting thehigh energy gas stream flow into shaft power, the second turbinerotating at a first speed and including less than or equal to about six(6) stages; a geared architecture driven by the second turbine; and apropulsor section driven by the second turbine through the gearedarchitecture at a second speed lower than the first speed, the propulsorsection including a fan with a pressure ratio across the fan sectionless than about 1.45, the propulsor section generating propulsive thrustas a mass flow rate of air through a bypass flow path from the shaftpower, wherein the fan includes a tip diameter greater than about fifty(50) inches and an Engine Unit Thrust Parameter (“EUTP”) defined as netengine thrust divided by a product of a mass flow rate of air throughthe bypass flow path, a tip diameter of the fan and the first rotationalspeed of the second turbine is less than about 0.30 at a take-offcondition.
 21. The turbofan engine as recited in claim 20, wherein theEUTP is less than about 0.25 at the take-off condition.
 22. The turbofanengine as recited in claim 20, wherein the EUTP is less than about 0.20at the take-off condition.
 23. The turbofan engine as recited in claim20, wherein the EUTP at one of a climb condition and a cruise conditionis less than about 0.10.
 24. The turbofan engine as recited in claim 20,wherein the EUTP at the take-off condition is less than about 0.08. 25.The gas turbofan engine as recited in claim 20, wherein the fan sectiondefines a bypass airflow having a bypass ratio greater than about ten(10).
 26. The turbofan engine as recited in claim 20, wherein the tipdiameter of the fan is between about 50 inches and about 160 inches. 27.The turbofan engine as recited in claim 20, wherein the mass flowgenerated by the propulsor section is between about 625 lbm/hour andabout 80,000 lbm/hour.
 28. The turbofan engine as recited in claim 20,wherein the first speed of the second turbine is between about 6200 rpmand about 12,500 rpm.
 29. The turbofan engine as recited in claim 20,wherein the second turbine comprises a low pressure turbine with 3 to 6stages.
 30. The turbofan engine as recited in claim 20, wherein a ratiobetween the number of fan blades and the number of rotors in the secondturbine is between about 3.3 and about 8.6.